There is a significant need for lower VOC-containing (volatile organic compound-containing) systems in the coatings industry due to increasing environmental restrictions. Typically, lower VOC-containing systems have been achieved by using lower molecular weight polymers. However, this can result in products having poorer performance.
In an effort to reduce the amount of VOC's released, and maintain performance, manufacturers have been using water-based polyurethanes. Such water-based polyurethanes are usually linear polymers and produce films that have chemical resistance lower than the highly crosslinked films of solvent-borne urethane systems. Preparing the polyurethane coating compositions by pre-crosslinking a water-based polyurethane polymer can be accomplished by incorporating a large amount of monomers that have more than two reactive functional groups in the prepolymer stage. However, this results in highly viscous prepolymer blends that cannot be easily dispersed in water. Diluents have been used to address this problem of viscosity, but many are highly irritating either to skin, eyes, or both. In many instances the presence of an “irritating” diluent will require that extensive industrial hygiene measures be undertaken before using the product. However, such measures may not be practical and such products may not be selected as a result.
Thus, what is needed are coating compositions that have high performance, low VOC levels, and low irritation levels.